It is estimated that 6 million people in this country chronically suffer from symptoms referable to coronary artery disease. Coronary arteriography is performed in more than 500,000 patients per year for consideration for mechanical interventions into their disease in order to improve quality of life, decrease drug related symptoms, or improve prognosis. Over half this number undergo either coronary artery bypass graft surgery (CABG) or percutantous transluminal coronary angioplasty (PTCA). Both techniques offer effective short term relief of symptoms with low morbidity and mortality rates. The long term results are less clear since there are significant restenosis rates within the first year for patients undergoing PTCA. In addition, patients 5-10 years following CABG have high incidences of both graft occlusion and progression of native coronary atherosclerosis. The current use of internal mammary grafts and antiplatelet agents may affect these results. PTCA has been demonstrated to be less costly than CABG in patients with single vessel LAD, however, this benefit has not been demonstrated in multivessel disease. All patients undergoing cardiac catheterization who have coronary artery disease will be asked to participate in the BARI registry. In the majority of these patients the clinical care will not be influenced but follow up data including symptomatic state, cost of intercurrent procedures, quality of life, and work status will be obtained at yearly intervals. Specific subgroups of patients will be defined for randomization to either PTCA or CABG. Thallium exercise testing will be performed at 6-8 weeks. At 3 month intervals following revascularization, similar follow up data to the non-randomized patients will be obtained. Repeat catheterization will be performed at 1 year. Yearly evaluations including thallium exercise testing and quality of life, symptoms, work status and cost of intercurrent procedures will be made. At the final year, coronary angiography will also be performed. The proposed Bypass Angioplasty Revascularization Investigation provides the framework to evaluate many of these important issues. The BARI registry will enable us to determine the natural history of both angioplasty and current surgical techniques over a prolonged period. The natural history of coronary artery disease in the 1980's and 1990's will also be determined as clinical decisions will not be influenced in the majority of these patients. The randomized subsets will allow for the rigorous study of these two revascularization techniques in selected patients. Given the widespread use of these procedures, this randomized trial to assess their efficacy is vitally needed.